1. Field of the Invention
This invention relates to a process for nitrosation of a compound selected from phenols and N,N-dialkylanilines to prepare the corresponding benzoquinone oximes or p-nitroso-N,N-dialkylanilines.
The standard processes for preparation of these nitrosated products comprise subjecting a phenol or a dialkylaniline to nitrosation reaction conditions using a nitrite ion in an aqueous system, wherein an acid stronger than nitrous acid acts on the nitrite to produce nitrous acid. The resulting nitrous acid is the actual nitrosating agent. In this connection, the process can be one of using nitrous acid itself instead of forming it "in situ" from a nitrite ion and a mineral acid, but this process is generally not practicable because of instability of the aqueous nitrous acid and the like.
Various methods have been used for carrying out such nitrosation reactions. From the industrial viewpoint, however, all conventional methods involve some problems or are otherwise not fully satisfactory.
2. Prior Art
The following processes are illustrative of representative conventional processes.
(1) Acetic acid solvent process (J. Chem. Soc. 1939 1808) PA0 (2) Alcohol solvent process (Org. Synthesis, Coll., Vol. 1, 511) PA0 (3) Aqueous solvent method (Ann. 277 85) PA0 (4) Nitrosation of dialkylanilines
This process comprises dissolving the starting phenol in a large amount (about 13-fold excess) of aqueous 50% acetic acid solution, and causing an aqueous solution of nitrite ion to act thereon. The reaction in such a dilute system gives rise to problems such as those relating to the efficiency per volume of reactors, the isolation and recovery of products, the recovery of the acetic acid used, and the losses upon recovery.
This process also uses large quantities of alcohol (about 5 times) and hydrochloric acid (about 5 times) on the basis of the starting phenol and entails the same problems as mentioned above. Especially, this process is accompanied by difficult problems in the recovery of products. More specifically, the nitrosated product is normally very soluble in alcohol, and it is generally recovered in a solid form by diluting the reaction liquid with a large amount of water. Thus, there arise problems in the recoveries of both the nitrosated product itself and the alcohol.
This process comprises causing an aqueous sulfuric acid solution to act on a dilute aqueous solution of a sodium salt of the starting phenol and sodium nitrite (wherein water is used in about 25-fold amount of the starting phenol). Water used as the solvent does not need to be recovered, but there exist significant problems in the efficiency per the volume of reactors and the recovery of product since the reaction is carried out in a very dilute system. The use of such a large amount of water is disadvantageous in that it is desirable from the viewpoint of preventing environmental pollution that the water used as the solvent be purified, although recovery of water is not necessary. If this reaction is carried out in a concentrated system, phenol, which has been formed as an intermediate in the course of the reaction, will be mixed with the nitrosated product in a pasty state, and the reaction will be discontinued.
One process of carrying out reaction uses a large amount (about 5-fold moles) of hydrochloric acid on the basis of the starting aniline in an aqueous solvent (Org. Synthesis, Coll. Vol. II, 223), and another process of carrying out reaction uses about 3-fold moles of hydrochloric acid, 2-fold moles of sodium nitrite and about 9-fold moles of acetic acid on the basis of the starting aniline [J. Chem. Soc., 1677 (1955)]. The products of these processes are in the form of the aniline hydrochloride, and an alkali treatment is required at the final stages of these reactions.